1. Field of the Invention
The invention relates to a flow control device for controlling the flow rate of a fluid, such as a chemical agent, dematerialized water, etc.
2. Background Art
FIG. 4 is a cross sectional view of a conventional flow control device, showing an example of a structure of the flow control device. This flow control device 1 is located in a fluid supply line for mixing a plurality of liquid agents, and also for controlling a flow rate of dematerialized water, etc., which is used in a product process for products. The flow control device is generally called a regulator.
A construction of the flow control device 1 will be explained more specifically. A housing 10 which forms the exterior of the flow control device 1 is formed by a material such as a resin, etc. An inlet port 21 and an outlet port 24 are arranged outside of the housing 10. Essential parts of the flow control device 1 are a valve seat 11 having an opening plane 11a which communicates with the inlet port 21, a valve body 30 which is movable perpendicular (upward and downward in FIG. 4) to the opening plane 11a of the valve seat 11, a diaphragm 35 which is fixed with the upper end of the valve body 30 so as to control a pressure, and a coil spring 36 which presses the valve body 30 to the valve seat 11, arranged inside of the housing 10. As shown in FIG. 4, the valve body 30 is separated into two portions.
A passage through which a fluid flows provides a first cavity 22 (generally called a valve chamber) and a second cavity 23 which communicates with the outlet port 24 between the valve seat 11 and the diaphragm 35. A pressure chamber 12 is arranged on one side, which opposes the second cavity 23, of the diaphragm 35; that is, the pressure chamber 12 is arranged at an upper side of the diaphragm 35 as shown in FIG. 4 and the pressure chamber 12 communicates with a pressure inlet port 13 which is formed in an upper part of the housing 10.
Additional constructions of the valve body 30 and functions of the valve body will be further explained.
The valve body 30 is movable upward and downward in FIG. 4 and is urged by the coil spring 36, which is arranged in a lower portion of the valve body 30, upwardly so as to touch the valve seat 11. According to the construction of the valve body 30 thus constructed, the opening plane 11a of the valve body 30 firmly contacts an outer surface of the valve body 30 so as to close the valve seat 11.
A top portion of the valve body 30 projects upward, and a male screw portion 30a is formed in the top portion thus projected. The valve body 30 is connected with the diaphragm 35 by engaging the male screw 30a with a female screw 35a which is formed in the diaphragm 35. Other constructions in which the valve body 30 is not connected with the diaphragm 35 are possible.
While urging fluid such as compressed air is supplied to the pressure inlet port 13, the pressure chamber 12 is pressurized and urges the diaphragm 35 downward by a force, caused by the compressed air, greater than an elastic force of the coil spring 36 which urges the diaphragm 35 upward. The diaphragm 35 thus urged moves the valve body 30 so as to depart from the valve seat 11 and also to open the opening plane 11a of the valve seat 11, and then, fluid in the first cavity 22 flows into the second cavity 23. A vertical moving distance of the valve body 30 is controlled due to the pressure of the fluid which presses the pressure chamber 12, and therefore, the flow rate of the fluid which flows through the opening plane of the valve seat 11 can be controlled by the pressure of the fluid. The fluid thus flowing into the second cavity 23 flows toward the outlet port 25, then a flow rate of the fluid which is supplied by the flow control device 1 is controlled.
The above flow control device 1 can block the flows of the fluid by closing the opening plane 11a of the valve seat 11 by the valve body 30 so as to close the passage fluid. However, the fluid tends to remain in the passage in the flow control device 1 and a flow line in which the flow control device 1 is arranged in a state in which the passage is closed by the valve body 30. Considering the fluid being retained in the flow control device 1, which is in a state in which the passage is closed, bacteria may grow, and such bacteria tend to cause adverse effects.
In order to discharge the fluid thus retained in the flow line, a bypass line may be arranged parallel to the flow control device 1. However, it is not possible to discharge the fluid retained in the flow control device 1 by the above bypass line, and a problem of complication of the fluid line arises.
Furthermore, another flow control device in which a bypass line for discharging a fluid is arranged therein has been designed. However, fluid may remain in a main passage between the ends of the bypass line, and therefore, further improvement which ensures discharge of the retained fluid is desired.
As another process for discharging the remaining fluid, it is possible to supply a small amount of compressed air to the pressure chamber 12 so as to move the diaphragm 35 and also to slightly open the opening plane 11a of the valve seat 11. However, because the above fluid control device 1 is designed for controlling a flow within a predetermined basic flow control rate and diaphragm 35, etc., are also designed for the predetermined basic control rate, it is difficult to control the flow rate for discharging the retained fluid which is below the predetermined basic flow control rate. That is, the diaphragm 35 which is specialized for the predetermined flow rate cannot control a small flow which is below the predetermined flow rate and cannot maintain stability of the flow.
In contrast, in a case where the diaphragm 35 is designed for controlling a slight flow, it becomes difficult to control the flow rate of fluid which flows at the predetermined basic control rate. That is, accuracy of flow control tends to be decreased by increasing the range of the control rate.
Because it is difficult to control the slight flow of the fluid in the conventional flow control device 1, it is necessary to flow the fluid through the flow control device 1 at the predetermined basic control rate in which a relatively large amount of fluid flows.